There are so many different effects of fatigue on performance that it has become really difficult to develop an understanding for why it occurs. Some of the symptoms are listed here on the screen. There's a reduced performance, well we know that. What you may not know, that there is also a decreased heart rate during exercise and this indicates the brain is unable to deliver the same amount of oxygen and nutrients to working muscles. There's an altered cognitive performance and this affects the decision making ability of the athlete. And workouts that used to feel easy become really, really hard to do. There is a reduced blood lactate concentration indicating that the glycolytic energy system has slowed down. And the athlete gets sick more frequently, suggesting that the immune system is overworked. And there is a disturbed quality of sleep. And the athlete also has an altered mood. Now scientists in various fields of study view all these symptoms of fatigue through slightly different lenses and offer alternative theories for about the cause of fatigue. For example, a biomechanist explains fatigue in terms of a decrease in maximal muscle force production, or an inability to sustain further exercise at a required force. And this is actually a definition of fatigue used in sport, so that's the biomechanist. A psychologist explains fatigue simply as a sensation of tiredness. They keep things very simple. And a physiologist defines fatigue in terms of a failure of a specific physiological system. And of course, naturally physiology people make things really really complicated. However, the commonality in all these views is that fatigue is a negative influence on the athlete's performance, eventually, leading to a termination of exercise due to events interfering with the ability of the active muscle to work properly. There are currently eight broad models offering an explanation for training-specific fatigue. These include the cardiovascular model. The energy supply or energy depletion model. The neuromuscular fatigue model. There's fatigue due to muscle trauma, that's another model. There's a biomechanical model. There's a thermoregulatory model. And there is a psychological or motivational model. And finally is the central governor model. Each of these models proposes a theory of explanation or viable explanation for the understanding causes of fatigue. Now Tim Noakes is a professor of exercise and sports science at the University if Cape Town. And he has written some really, really interesting stuff about the insights and provided neat insights about each of this models of fatigue. So the lesson here I draw from his particular writings.